Production of high tenacity cellulose derivative yarns



Patented Aug. 9, 1949 PRODUCTION OF HIGH TENACITY CELLU- LOSE DERIVATIVE YARNS Richard R. Sitzler, Cumberland, Md., assignor to Celanese Corporation of America, a corporation of Delaware No Drawing. Application October 5, 1945, Serial No. 620,625

7 Claims.

This invention relates to high tenacity yarns and filaments and relates more particularly to the production of high tenacity regenerated cellulose yarns and filaments prepared by the stretching and saponification of yarns and filaments having a basis of cellulose acetate or other organic ester of cellulose.

An object of this invention is the provision of an eficient and economical process for the production of high tenacity regenerated cellulose yarns and filaments having improved textile processing characteristics.

Another object of this invention is the preparation of yarns and filaments having a basis of cellulose acetate or other organic acid ester of cellulose capable of being subjected to a more uniform degree of stretching under the influence of a suitable softening medium.

A further object of this invention is the production of improved fabrics woven of high tenacity regenerated cellulose yarns and filaments.

Other objects of this invention will appear from the following detailed description.

Yarns of high tenacity have been produced by stretching yarns having a basis of cellulose acetate, or other organic ester of cellulose, and prepared by dry spinning operations. The stretching is effected by exerting a tension on the yarns, which are usually of a relatively high denier, i. e. 450 to 1500, prior to stretching, while 1 they are under the influence of a softening agent such as steam, hot water, or a liquid containing an organic solvent or softening agent for the organic ester of cellulose material. During the stretching operation the length of the yarns may be increased to the extent of 200, 300, 500, or even 1000 or 2000% of their original length, their denier being, of course, correspondingly decreased.

The increase in tenacity achieved by the stretching operation is retained and is even enhanced when such stretched organic ester of cellulose yarns are subjected to the action of saponifying baths and converted to regenerated cellulose yarns. The stretching operation is mosteconomically effected with the yarns travelling at high speeds, and must be conducted in such a manner as to produce a yarn of as nearly uniform physical characteristics, e. g. denier, tenacity, etc., as is possible. Uniformity in the stretched yarns prior to saponification is dependent upon attaining a substantially uniform degree of plasticity in the yarns while they are under the influence of the softening agent so that a uniform degree of stretch will be achieved all along the length of the yarn. This uniformity in the plasticity of the yarns is not always attained due to the fact that the yarn at different portions along the length thereof often contains different amounts of residual volatile solvent, which solvent is left in the yarn in the process of preparin the same. As a result of this condition in the yarn, the plasticity thereof, under the influence of the softening medium employed durin the stretching operation, will vary, thus causing non-uniform stretching and yielding a yarn having variations in the physical characteristics. When such stretched yarns are saponified and woven into fabrics, they exhibit undesirable faults.

I have found that the above and other disadvantages encountered in the production of high tenacity regenerated cellulose yarns by processes involving the stretching and saponification of yarns having a basis of cellulose acetate or other organic acid ester of cellulose may now be overcome. In accordance with my novel process, improved high tenacity regenerated cellulose yarns may be obtained by incorporating a non-volatile plasticizer in the cellulose acetate or other organic acid ester of cellulose yarns prior to stretching and, after stretching the yarns while they are under the influence of a suitable softening medium, subjecting them to saponification to yield the desired regenerated cellulose yarns. The incorporation of said nonvolatile plasticizer in the cellulose acetate or other organic acid ester of cellulose yarns imparts a substantially uniform degree of plasticity to the yarns so formed. When stretched under the influence of a softening agent, stretched cellulose acetate or other organic ester of cellulose yarns of an unusual degree of uniformity are obtained. The uniform character of the stretched cellulose acetate or other organic acid ester of cellulose yarns is entirely retained upon saponification and the physical characteristics of the high tenacity regenerated cellulose yarns produced by the saponification of said stretched yarns have a uniformity greater than has heretofore been attained.

While any suitable plasticizer for cellulose acetate or other organic ester of cellulose may be incorporated in the yarns in accordance with the novel process of my invention, I preferably employ a substantially Water-insoluble, non-volatile plasticizer which is saponifiable under the action of the basic saponifying agent employed for saponifying the cellulose ester base material and which on hydrolysis yields water-soluble fission products. Thus, since the fission products produced by saponification of the plasticizer present in the yarns are water-soluble, they will be removed in the saponifying medium. The high tenacity regenerated cellulose yarns obtained will therefore be entirely free of plasticizer since saponification of the cellulose ester material and the plasticizer take place concurrently. Thus, my novel process has an added advantage since the high tenacity regenerated cellulose yarns may be taken up directly in any convenient manner without the necessity of removing the plasticizer originally incorporated in the cellulose acetate or other organic acid ester of cellulose yarn. As examples of the water-insoluble, non-volatile plasticizers, which are saponifiable to water-soluble products, employed in accordance with my novel process, there may be mentioned acetyl triethyl citrate, diethyl succinate, diethyl tartrate, tri-ethylene glycol dipropionate, triacetin, or tripropionin.

The plasticizer may conveniently be incorporated in the spinning solution from which the cellulose acetate or other organic acid ester of cellulose filaments are formed by the usual dry spinning operations wherein a solution comprising cellulose acetate or other organic acid ester of cellulose dissolved in a volatile solvent is extruded through a spinneret into an evaporative atmosphere. The amount of plasticizer employed may vary but the most advantageous results are obtained Where an amount of from 0.5 to 5% on the Weight of the cellulose acetate or other organic acidester of cellulose incorporated in the spinning dope.

The plasticized yarns which are subjected to stretching may have a basis of cellulose acetate or any other organic acid ester of cellulose. Examples of other organic acid esters of cellulose are cellulose propionate, cellulose butyrate, as well as mixed esters of cellulose, such as, cellulose aceto-propionate and cellulose aceto-butyrate.

The stretched organic ester of cellulose yarns containing the plasticizer may be saponified conveniently to yield high tenacity regenerated cellulose yarns employing batch processes, with the stretched yarns wound on bobbins. Continuous processes may also be employed, wherein the stretched organic ester of cellulose yarns may be led directly into a saponifying bath, the path through the saponifying bath being of sufficient length so that the yarn is completely saponified before leaving the bath. After saponification, the regenerated cellulose yarn, now free of plasticizers, is washed free of the saponifying agent, dried and wound into packages of convenient size.

The saponification may be carried out by means of any suitable basic agent. The saponifying agent may be inorganic in nature, such as, for example, sodiumhydroxide, potassium hydroxide, sodium silicate, ammonium hydroxide, sodium carbonate, or other inorganic basic agent. Organic saponifying agents may also be employed such as, for example, methylamine, ethylene diamine, triethanolamine or other organic bases. The saponifying agents may be employed in varying concentrations in aqueous, alcoholic or aqueous-alcoholic solutions. The saponifying bath may be at a temperature of to 100 C'. For example, when aqueous solutions of sodium hydroxide are employed, they may be of concentration of 0.1 to 5% by weight and saponification may be eifected in from to 180 minutes with the solution at 30 to 90 C. When employing aqueous solutions of sodium hydroxide as the saponifying medium, it is preferable to include a salt such as sodium chloride or sodium acetate in said solution.

In order further to illustrate my invention but without being limited thereto, the following example is given:

A 432 denier, 40 filament cellulose acetate yarn is dry spun from a solution containing 26% cellulose acetate in 95/5 acetone/water containing 2% on the weight of the cellulose acetate of acetyl triethyl citrate by extruding said solution through a spinneret into an evaporative atmosphere. The yarn is stretched 9 times its original length while under the softening action of steam under pressure, to yield a 48 denier, 40 filament cellulose acetate yarn and is then subjected to saponification. The saponification is effected by employing a 0.6% aqueous solution of sodium hydroxide at a temperature of C. and maintaining the yarn in contact therewith for '75 minutes. High tenacity, regenerated cellulose yarns of an average tenacity of about 6 grams per denier are obtained. Very little deviation from the average tenacity of the yarns is found when random portions of the yarn are subjected to tenacity tests. In addition to the highly uniform character of the regenerated cellulose yarns produced, the latter have exceptionally good Weaving properties, no difficulties being experienced during warping or beaming down, with the yarns yielding an unusually small number of slubs, due to filament breakage. The general appearance, hand and draping qualities of the woven fabric are excellent.

It is to be understood that the foregoing detailed description is given merely by way of illustration and that many variations may be made therein without departing from the spirit of my invention.

Having described my invention, what I desire to secure by Letters Patent is:

1. In a process for the production of improved high tenacity cellulosic yarns, the steps which comprise incorporating a non-volatile, substantially water-insoluble plasticizer saponifiable to water-soluble products in a yarn having a basis of an organic acid ester of cellulose, stretching the plasticized yarn in the presence of a softening medium therefor, and completely saponifying the stretched, plasticized organic acid ester of cellulose yarn containing substantially all of the plasticizer incorporated therein whereby a plasticizer-free regenerated cellulose yarn is obtained.

2. In a process for the production of improved high tenacity cellulosic yarns, the steps which comprise incorporating a nonvolatile, substantially water-insoluble plasticizer saponifiable to water soluble products in a yarn having a basis of cellulose acetate, stretching the plasticized yarn in the presence of a softening medium therefor, and completely saponifying the stretched, plasticized cellulose acetate yarn containing substantially all of the plasticizer incorporated therein whereby a plasticizer-free regenerated cellulose yarn is obtained.

3. In a process for the production of improved high tenacity cellulosic yarns, the steps which comprise incorporating from 0.5 to 5% by weight of a non-volatile, substantially water-insoluble plasticizer saponifiable to water-soluble products in a yarn having a basis of an organic acid ester of cellulose, stretching the plasticized yarn in the presence of a softening medium therefor, and completely saponifying the stretched, plasticized organic acid ester of cellulose yarn containing substantially all of the plasticizer incorporated therein whereby a plasticizer-free regenerated cellulose yarn is obtained.

4. In a process for the production of improved high tenacity celluiosic yarns, the steps which comprise incorporating from 0.5 to 5% by Weight of a non-volatile, substantially water-insoluble plasticizer saponifiable to water-soluble products, in a yarn having a basis of cellulose acetate, stretching the plasticized yarn in the presence of a softening medium therefor, and completely saponifying the stretched, plasticized celiulose acetate yarn containing substantially all of the plasticizer incorporated therein whereby a plasticizer-free regenerated cellulose yarn is obtained.

5. In a process for the production of improved high tenacity cellulosic yarns, the steps which comprise incorporating from 0.5 to 5% by weight of acetyl triethyl citrate, in a yarn having a basis of cellulose acetate, stretching the plasticized yarn in the presence of a softening medium therefor, and completely saponifying the stretched,

lastioized cellulose acetate yarn containing substantially all of the plasticizer incorporated therein whereby a plasticizer-free regenerated cellulose yarn is obtained.

6. In a process for the production of improved high tenacity cellulosic yarns, the steps which comprise incorporating from 0.5 to 5% by weight of triethylene glycol dipropionate, in a yarn having a basis of cellulose acetate, stretching the plasticized yarn in the presence of a softening REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,053,766 Dreyfus Sept. 8, 1936 2,142,722 Dreyfus et al Jan. 3, 1939 2,147,640 Dickie et a1 Feb. 21, 1%39 2,155,411 Dreyfus Apr. 25, 1939 FOREIGN PATENTS Number Country Date 340,456 Great Britain Jan. 1, 1931 438,584 Great Britain Nov, 12, 1935 469,749 Great Britain July 26, 1937 OTHER REFERENCES "Hercules Cellulose Acetate, pamphlet, 1941, page 16. (Copy in Division 64.) 

